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module ActiveModel::AttributeMethods
Active Model Attribute Methods
Provides a way to add prefixes and suffixes to your methods as well as handling the creation of ActiveRecord::Base-like class methods such as table_name.
The requirements to implement ActiveModel::AttributeMethods are to:
include ActiveModel::AttributeMethodsin your class.Call each of its methods you want to add, such as
attribute_method_suffixorattribute_method_prefix.Call
define_attribute_methodsafter the other methods are called.Define the various generic
_attributemethods that you have declared.Define an
attributesmethod which returns a hash with each attribute name in your model as hash key and the attribute value as hash value. Hash keys must be strings.
A minimal implementation could be:
class Person
include ActiveModel::AttributeMethods
attribute_method_affix prefix: 'reset_', suffix: '_to_default!'
attribute_method_suffix '_contrived?'
attribute_method_prefix 'clear_'
define_attribute_methods :name
attr_accessor :name
def attributes
{ 'name' => @name }
end
private
def attribute_contrived?(attr)
true
end
def clear_attribute(attr)
send("#{attr}=", nil)
end
def reset_attribute_to_default!(attr)
send("#{attr}=", 'Default Name')
end
end
Constants
- CALL_COMPILABLE_REGEXP
- NAME_COMPILABLE_REGEXP
Public Instance Methods
# File activemodel/lib/active_model/attribute_methods.rb, line 440
def attribute_missing(match, *args, &block)
__send__(match.target, match.attr_name, *args, &block)
end
attribute_missing is like method_missing, but for attributes. When method_missing is called we check to see if there is a matching attribute method. If so, we tell attribute_missing to dispatch the attribute. This method can be overloaded to customize the behavior.
# File activemodel/lib/active_model/attribute_methods.rb, line 427
def method_missing(method, *args, &block)
if respond_to_without_attributes?(method, true)
super
else
match = matched_attribute_method(method.to_s)
match ? attribute_missing(match, *args, &block) : super
end
end
Allows access to the object attributes, which are held in the hash returned by attributes, as though they were first-class methods. So a Person class with a name attribute can for example use Person#name and Person#name= and never directly use the attributes hash – except for multiple assignments with ActiveRecord::Base#attributes=.
It's also possible to instantiate related objects, so a Client class belonging to the clients table with a master_id foreign key can instantiate master through Client#master.
# File activemodel/lib/active_model/attribute_methods.rb, line 448
def respond_to?(method, include_private_methods = false)
if super
true
elsif !include_private_methods && super(method, true)
# If we're here then we haven't found among non-private methods
# but found among all methods. Which means that the given method is private.
false
else
!matched_attribute_method(method.to_s).nil?
end
end
A Person instance with a name attribute can ask person.respond_to?(:name), person.respond_to?(:name=), and person.respond_to?(:name?) which will all return true.
© 2004–2018 David Heinemeier Hansson
Licensed under the MIT License.